The large (>330 kb) dsDNA, plaque-forming chlorella viruses have provided new and unexpected gene products for the past 20 years, including several medically relevant proteins. The objectives of this proposal are a step toward the long-term goal of understanding the structural and functional aspects of these viruses, as well as their associated genes and gene products. Many chlorella virus proteins are the smallest representatives of their functional class. Consequently, some of these proteins are the subject of intense physical and biochemical investigation, e.g. a type II DNA topoisomerase and a potassium ion channel protein Kcv. This proposal focuses on two important problems associated with virus entry into the cell and maturation of progeny viruses. The specific aims of this proposal are to: i) examine kcv genes and their corresponding proteins from a broad range of chlorella viruses as an alternate approach for exploring structure/function relationships in potassium ion channels and ii) evaluate unusual virus-encoded posttranslational modifications of the virus major capsid protein, Vp54. In addition to characterizing the seven putative virus-encoded glycosyltransferases, the structures of the six glycans attached to the major capsid protein will be determined. The viral proteins will be investigated at physiological, molecular biological and biochemical levels, including structural analyses. These studies are expected to reveal new concepts in intra- and inter-molecular interactions of potassium ion channels, and also novel mechanisms for protein glycosylation and myristoylation. Phylogenetic analyses indicate the genetically diverse but morphologically indistinguishable chlorella viruses have a long evolutionary history, possibly dating back to the time eukaryotes and prokaryotes separated. Thus, chlorella viruses are an important model for studying large nucleocytoplasmic dsDNA viruses because they have evolutionary ties to important mammalian viruses, such as the pox viruses and the quarantined African swine fever virus.